In multistoried apartments or buildings, transmission of floor impact sounds from the upper stories to the room located directly below causes troubles frequently. Such floor impact sounds are generally divided into two groups, i.e., light-weight floor impact sounds produced by occupant activity such as walking and, heavy floor impact sounds produced by sharp transient type impulses such as those caused by falling objects or jump-off of a child. The former, light-weight floor impact sounds can be reduced with ease by constituting a finish floor with soft or flexible finish floorings such as carpets since such finish floorings absorb the light-weight impacts effectively.
It is, however, very difficult with such finish floorings to reduce the heavy floor impact sounds effectively. The heavy impact forces are too large for the soft finish floorings and are scarcely absorbed by the finish floor. Thus, the heavy impact forces are directly transmitted to the concrete slab through the floor panels, thereby causing vibration of the concrete slab at low frequencies, which in turn causes production of heavy floor impact sounds.
As a means for reducing the transmission of impact forces to the concrete slab, there has been known a floating floor constructed by laying buffer members such as glass wool mats on a floor slab such as concrete slabs, arranging floor joists on the buffer members at proper intervals, laying floor panels on the floor joists to form a floating floor, and then covering the same with finish floorings. In such a floating floor, a heavy impact force applied to a point of the finish floor is distributed over several floor joists through the floor panel and then transmitted to the buffer members. The transmitted force is then absorbed and weakened to some degree by deformation of the buffer members, thus making it possible to reduce the forces directly acting on the concrete slab.
However, it is impossible with the above floating floor to obtain satisfactory sound insulating characteristics. Since the floating floor has a space formed between the floor panels and buffer members, the floor panels are easy to produce flexural deformation by the heavy impact. For this reason, the heavy floor impact produces a large flexural vibration of the floor panels, which is easy to propagate through the floor slab to the room located directly below. Also, the flexural deformation of the floor panel causes spontaneous compression of the air under the floor panels, resulting in increase in air pressure. The pressure of the compressed air acts alternately on the underside of the floor panel and the upperside of the buffer members, and causes vibration of the floor slab. Furthermore, if any heavy impact force is applied to one of the floor panels, its flexural vibration is propagated to the other floor panels through the floor joists since the floor panels are mounted in parallel on the assembled floor joists. In addition, since the individual floor joists are required to be arranged on the soft buffer members, it is difficult with the prior art to keep the floor joists in their fixed positions during construction work. Thus, the use of joists makes it difficult to improve efficiency of work.